The Pentagon has placed 8,500 troops on heightened alert to potentially deploy to Eastern Europe over concerns Russia may soon invade Ukraine. The U.S. and NATO allies have accused Russia of amassing 100,000 troops near the Ukrainian border, but Russia has denied it’s planning an invasion. White House Press Secretary Jen Psaki spoke Monday.

Press Secretary Jen Psaki: “And we have a sacred obligation to support the security of our eastern flank countries. I think it’s important to remember who the aggressor is here. It is not the United States. It is not these eastern flank countries. It is Russia, who has tens of thousands of troops on the border of Ukraine.”

This comes as other NATO nations are planning to send additional troops, ships and fighter jets to Eastern Europe. On Monday, the Kremlin accused the United States and NATO of escalating tension in the region. Meanwhile, negotiations to resolve the crisis are ongoing, with officials from Russia, Ukraine, France and Germany scheduled to meet in Paris on Wednesday.